The present invention relates to continuous casting of metal alloys.
In particular, the present invention relates to horizontal continuous casting of metal alloys which during and immediately subsequent to solidifying tend to have a component thereof separate from the metal in vapor form.
The present invention relates in particular to the continuous horizontal casting of a brass alloy as well as to an apparatus for carrying out the method of horizontal casting.
During continuous casting of alloys of the above type it is difficult to achieve faultless elongated castings during long periods of operation. Such castings have cracks and rough portions at their exterior surface while also having a diameter which diminishes in size along the length of the casting. The reason for these drawbacks resides in the fact that during and shortly after solidification of the metal alloy a component thereof separates therefrom in vapor form, and this vapor results in deposits at the inner surface of the mold. In fact it has been observed that during continuous casting of such alloys there is a deposition out of the glowing casting, this deposition resulting in formation of deposits which cling very tightly to the inner surface of the mold. As a result of these deposits, the resistance to travel of the metal through the mold at the region where the metal still engages the inner surface of the mold continuously increases, so that to an increasing extent as the molding operation continues there are formation of cracks in the surface of the casting, with the still relatively thin skin of solidified metal at the outer portion of the casting tending to fuse itself together to a greater or lesser extent where such cracks are formed, and with the diameter of the casting progressively becoming of a smaller size.
As a result, aside from frequent changes of the mold, it is necessary before further operations are performed on such castings to remove from the outer surface thereof a layer of metal having a thickness of several millimeters, so that the result is additional labor costs and loss of material.
During vertical continuous casting where the mold is independent of a furnace, or in other words with an open mold, it is possible to some extent to avoid these drawbacks by providing at the surface of the molten metal suitable lubricating and separating agents which will at least to some extent avoid the formation of such deposits. Thus, with such measures it is possible to obtain a satisfactory product at least with relatively large-diameter castings.
When continuous casting is carried out with an alloy such as, for example, brass, it is already known that it is advisable to cover the surface of the molten metal at the top of the vertical mold with a combustible gas. For this purpose use is made of a burner having ring-shaped slots and arranged with respect to the surface of the molten metal in such a way that the combustible gas is delivered in the form of an uninterrupted film against the inner surface of the mold, so as to achieve in this way a protective atmosphere which prevents oxidation of the molten metal surface.
Also, in order to provide and maintain a protective atmosphere it is known to utilize a partially removable hood charged with a protective gas from lateral pipes, with this hood being arranged over the supply pipes, troughs for the molten metal, and mold in such a way that upon raising part of the hood so as to obtain access to the troughs the supply pipes still remain beneath the protective gas.
However, the fact is that measures of the above type are limited only to vertical continuous casting. Such procedures cannot be used with horizontal continuous casting which to an increasing extent is being more widely utilized because of the relatively small vertical space which is required by a horizontal casting apparatus and because of the uninterrupted nature of the operation of a horizontal continuous casting apparatus.
It is also known when carrying out vertical continuous casting with a mold which is independent of a furnace, to provide a combustible, carbon-containing gas between the freshly-formed casting skin of the solidifying metal and the surface of the mold at a location beneath the elevation where the metal starts to solidify, this latter combustible, carbon-containing gas being supplied with an amount of air which is insufficient for combustion of the gas so that as a result of the incomplete combustion carbon deposits itself between the skin of the solidifying casting and the mold to serve as a lubricant. In accordance with other operating procedures, it is known to feed into the space between the shrinking casting and the mold a gas under pressure together with oil or other lubricant, with this gas being an inert gas such as nitrogen or hydrogen. These procedures of course represent attempts to maintain the solidifying metal as well as the molten metal of the runner away from the mold wall by way of the lubricant or, in some cases, the layer of inert gas.
In addition, access of the slag between the metal and mold wall is to be avoided. In order to maintain the pressure required for this purpose, and in any case in order to be sure that the gas flows upwardly, an annular seal is provided at the discharge end of the vertical mold, surrounding the casting which issues downwardly through this discharge end.
However, such measures cannot be used with horizontal continuous casting where the mold must be in communication with the furnace or other source of molten metal. The result of utilizing such measures in horizontal continuous casting is that the lubricant and gas reaches the molten metal and forms therein inclusions of carbon, gaseous expansions and blowholes, which during the continuing casting operation travel into the solidifying casting to form undesirable foreign bodies therein as well as cavitations and blowholes. Thus it is impossible to achieve a faultless inner structure or matrix for such castings, and the result is that all that remains to be achieved is at least a clean, crack-free outer surface for the elongated casting body.